In a 2005 poll carried out by the BBC Radio show “In Our Time”, Karl Marx was voted the greatest philosopher of all time, winning more than double the number of votes of the second place thinker (David Hume). Marx would likely have been bemused – and perhaps even somewhat exasperated – by this, given the recurring aspersions he cast on philosophy and philosophers throughout much of his life. Yet Marx’s relation to philosophy is by no means straightforward, as the contributions to this issue demonstrate. While Marx struggled against it (most emphatically in his earlier writings), denouncing its distortions, parochialism, and impotence, philosophy remained a crucial reference point for him throughout his life, even long after he had apparently left it behind. Philosophy, too, has not been left untouched by this encounter, having irretrievably lost something of its naivety and self-satisfaction as a result of Marx’s famous claim that rather than merely interpreting the world (as philosophers have done), the point is to change it.